Rubber modified styrene-containing resin has good processability, high impact strength, and good appearance. Accordingly, the resin has been widely applied in the manufacture of electrical appliances and office supplies. When rubber modified styrene-containing resin is used in personal computers, facsimiles, and the like which emit heat, flame-retardance is required of the resin due to combustibility.
A widely known method for the flame retardancy is the addition of halogen-containing compounds or antimony-containing compounds to a rubber modified styrene-containing resin to impart flame retardance. The methods for improvement of flame-retardant property by applying halogen- and antimony-containing compound have advantages such as easy acquisition of flame retardance and no degradation of the physical properties. However, it was observed that the halogen-containing compound results in the corrosion of the mold itself by the hydrogen halide gases released during the molding process. These potentially fatal toxic gases are liberated in case of fire. Since a polybromodiphenyl ether, mainly used for a halogen-containing flame retardant, can produce toxic gases such as dioxin or furan during combustion, flame retardants which are not prepared with halogen-containing compound have become main concerns in this field.
It is commonly known a method to apply phosphorus or nitrogen compounds as halogen-free flame retardant to a resin composition. However, use of only phosphorus compound reduces the heat resistance of a rubber modified styrene-containing resin and does not impart sufficient flame retardance. Generally, when a rubber modified styrene-containing resin such as ABS is burned, a char is not produced due to decomposition and vaporization in most parts (Journal of Applied Polymer Science, 1998, vol. 68, p. 1067). Therefore, to impart flame retardancy, it is necessary to add a char-forming agent to a resin composition.
Japanese Patent Laid-open No. 7-48491 discloses a flameproof thermoplastic resin, made by adding a novolac phenolic resin and a phosphoric acid ester into a thermoplastic copolymer resin composed of a rubber copolymer and an aromatic vinyl monomer. It was found that in order to obtain a good property of flame retardancy, a phenolic resin as a char-forming agent and a phosphoric acid ester compound as a flame retardant should be added in relatively large amounts. However, in this case, the heat resistance and the mechanical strength such as impact strength of the resin composition are reduced.
U.S. Pat. No. 4,526,917 discloses that TPP and a mono phosphoric acid ester compound having a mesityl group are added to a base resin comprised a polyphenylene ether resin and a styrenic resin. However, the amount of polyphenylene ether is increased to improve a flame retardancy, so a flowability of the resin composition is decreased.
U.S. Pat. No. 4,503,178 disclosed cyclic phosphine oxides that are useful as flame retardants for styrene modified polyphenylene ether resins. Cyclic phosphinyl-carboxylic acid derivatives are not disclosed.
U.S. Pat. No. 4,081,463 relates to the production of 2-carboxyethyl(phenyl)phosphinic acid which is useful as a flame retardant with organic polymers such as polyester.
U.S. Pat. No. 5,334,760 discloses that a ring-opened oxaphospholane can be used as a flame retardant for polyester. A phosphinyl-carboxylic acid derivative in the form of a cyclic acid anhydride is also disclosed. The flame retardants are disclosed as being useful for polyester.
German Patent Laid-Open No. 28 36 771 discloses that a cyclic phosphate can be used as a flame retardant. The cyclic phosphate does not contain any carboxylic acid portion.
The present inventors disclosed a flame retardant thermoplastic resin composition containing no phenolic resin in order to solve the previously discussed problems in Korean Patent Application Nos. 1999-028442 and 1999-028443, herein incorporated by reference. The resin compositions disclosed in these patent application comprise a blend of a rubber-modified styrene-containing resin and a polyphenylene ether resin as a base resin, a styrene-acrylonitrile (SAN) copolymer having from 5 to 18% by weight of acrylonitrile as a compatibilizer to improve heat resistance and flame retardance and a phosphoric acid ester compound as a flame-retardant to improve flame retardance property without decrease of mechanical properties.
Resin compositions containing an oxaphospholane compound as a non-halogen flame retardant in a base resin comprised of rubber modified polystyrene resin and polyphenylene ether are disclosed in commonly owned Ser. No. 10/231,448, herein incorporated by reference.
The thermoplastic resin compositions according to the present invention having highly improved flame retardance are obtained by adding an oxaphospholane compound alone or in combination with a phosphoric acid ester compound as a flame retardant to a blend of a rubber-modified styrene-containing resin, a polyphenylene ether resin, and a compatabilizer. The thermoplastic resin compositions according to the present invention have good mechanical properties, heat resistance, and flame retardance.